sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, white, and rusty orange/red; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, white, and rusty orange/red
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, white, and rusty orange/red; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed in marine or freshwater environments via the accumulation of siliceous remains of organisms or chemical precipitation. The iron staining (red/orange) occurs through subsequent weathering and oxidation.
Uses & applications
Historically used for stone tools and fire-starting. Currently used as road aggregate, architectural stone, and occasionally for lapidary crafts.
Geological facts
Chert is essentially a variety of flint. It is so tough and resistant to weathering that it often remains in soil long after the surrounding limestone has dissolved away.
Field identification & locations
Identified by its extreme hardness (scratches glass), smooth conchoidal fracture, and dull/opaque appearance. Commonly found as nodules in limestone or as stream gravel.
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